Induction melting furnace



NOV. 24, 1959 w, KANN 2,914,593

INDUCTION MEL-TING FURNACE Filed Jan. 22, 1958 4 Sheets-Sheet 1 ATTOR/VEKS' Nov. 24, 1959 Filed Jan.

W. L. KANN INDUCTION MELTING FURNACE 22, 1958 4 Sheets-Sheet 2 INVENTOR.

Mil/4M (IA/N W. L. KANN INDUCTION MELTING FURNACE Nov. 24, 1959 4 Sheets-Sheet 5 Filed Jan. 22. 1958 m 1 m M a M d M J y W L 1 3 E P Lh// BY W ##4## AffOR/VEYS Nov. 24, 1959 w. L. KANN INDUCTION MELTING FURNACE 4 Sheets-Sheet 4 Filed Jan. 22, 1958 v iiifls ates Patent INDUCTION MELTIN G FURNACE William L; Kann, Pittsburgh, Pa., assignor to Steel Shot Producers, Incorporated, Butler, Pa., a corporation of Pennsylvania Application January 22, 1958, Serial No. 710,443

7 Claims. 01. 13-27 The present invention relates to an electric induction furnace especially adapted for melting metals.

The invention is an improvement on the type of furnace shown generally in expired Patent No. 1,895,421, which issued on January 24, 1933 to E. F. Northrup. In furnaces of this type, as they have been commercially known on the market, the induction coil has been a water-cooled coil of the type illustrated in the above Northrup patent. In building up the heat-insulation material on the inside of this coil, a layer of air-dried heat insulating cement has first been applied to the inner surface of the induction coil as indicated at 16 in the patent. Inside of this shell 16 of air-dried cement, there has been built up a lining of finely-divided refractory material as indicated at 11 in the Northrup patent. Usually this lining has been rammed or compacted between the layer 16 and an inner crucible or form as shown at in the patent. In most cases, the form or crucible has been removed prior to actual use of the furnace, and upon melting the first charge of metal in the furnace, the finelydivided refractory becomes sintered into a substantially unitary furnace lining.

In the prior art induction furnaces referred to, the linings have been built up within an outer housing so that the lined induction coil and the housing both form integral parts of a unitary furnace.

In order to avoid interference with the electrical characteristics of the induction coil, it has been usual in these prior-art furnaces to form the framework of the housing, and the supports for the induction coil, largely from wooden timbers, and since these furnaces are relatively large and heavy, it has been necessary to employ fairly large timbers. Any metal reinforcing that has beenused has been formed of non-magnetic steel such as manganese steel. I

The above construction is subject to a number of ditficulties. In the first place, the copper induction coil itself expands and contracts with alternate heating and cooling. The framework and outer container likewise expand and contract, and as the furnace is tilted for pouring,

the heavy framework and housing are subjected to twisting stresses. As a result of these forces, it is inevitable that eventually there appear in the furnace lining cracks which permit metal to run out. Such a run out of hot metal sets on fire the wood members of the framework, and usually burns up a considerable portion of the framework. The furnace may then be down for several weeks while the furnace is re-lined and re-wooded, i.e., the burned timbers are replaced.

After the furnace is re-wooded, it is then necessary to re-line the induction coil with the insulating layers as described above. This is a tedious and difficult task, due to the fact that the induction coil is permanently located within the housing and therefore is not readily accessible.

One object of the present invention is to provide an induction melting furnace of the above type, in which no wood or other combustible material is used in the 2,914,593 Patented Nov. 24, 1959 no twisting of the casing when the furnace is tilted for pouring. This reduces the twisting stresses and reduces materially the appearances of cracks in the furnace lining.

Another feature of the invention resides in the fact that the induction coil, together with its heat insulating linings, is formed as a separate self-contained unit that may be readily removed from and replaced in the furnace housing. This construction makes it much easier to form the insulating linings within the induction coil, and in case the lining of a furnace does become cracked or needs replacement for some other reason, it is a very simple and easy operation to remove the coil unit from the furnace and replace it with another coil unit that has been previously fabricated and is ready for use as a replacement unit.

In a preferred embodiment of the invention the turns of the induction coil are held together as a unit by clamping them to a number of vertical legs, which in turn are fastened to pieces secured to the frame. The coil can readily be removed as a unit by unbolting the legs from the frame and lifting the coil from the housing.

The plate carrying the operating connections is also made so that only a few connections need be broken in removing the coil.

These and other objects and advantages of the invention will become apparent as the description proceeds.

The present application is in part a continuation of my co-pending application Ser. No. 372,741, filed August 6, 1953.

In the drawings:

Fig. 1 is a top invention.

Fig. 2 is a side elevation of the furnace shown in Fig. 1.

Fig. 3 is a front elevation of the furnace.

Fig. 4 is a section on line IV-IV of Fig. 5.

Fig. 5 is a vertical section through the furnace.

Fig. 6 is a section on line VI-VI of Fig. 4.

Fig. 7 is a fragmentary section of the coil mounting.

In the following description a preferred embodiment of the invention will be described in detail for purposes of illustration only.

Referring more particularly to Figs. 4 and 5, it will be seen that the induction coil 10 is of usual size and shape, and since the construction of this coil forms no part of the present invention, it will not be described in detail. The coil may be made of any preferred material but is usually of copper. Extensions 11 which project from the coil permit attachment of suitable electrical and cooling connections. The entire coil for the furnace as illustrated is for convenience built up of two separate sections located one above the other, but obviously the coil could be formed as a single continuous coil if desired.

The coil is formed into a separate, replaceable unit, by having its turns clamped firmly against the legs 12. As illustrated there are six of these legs, but obviously this number may be varied as preferred. Each leg 12 is formed of a piece of mill board 2 in. thick by 6 in. Wide and of suitable length. The inner edge of each leg is formed with a series of semi-circular indentations 13 plan view of a furnace embodying the which are spaced apart so as to receive the turns of the .coil 10.

of mill board and are secured in place by brass bolts 15 which extend through the wedge pieces 14 and through the legs .12.

In this manner the legs 12 hold the turns of coil inproper spaced relation to each other, and at the sametime tie them together into a self-supporting unit which canbe readily transported and inserted into'the furnace ou in After the induction coil has been clamped to the legs 12 as just described, a layer of refractory cement 16 is applied to the inside of the coil as shown especially in Fig 6 This refractory cement may be an air-drying cement and is plastered in plastic condition on the. inside of the coil. After the refractory cement lohas set and has become hardened, the next step is to form the inner refractory lining. I'

This is done by first placinginside the coil a cruciblelike form 17 which serves to define the well or metal holding portion of the finished crucible. After the form 17 is properly positioned, the space between it and the coat ofrefractory cement 16 is filled with a suitable finely divided refractory. material. This refractory powder is poured into the'open space, a small layer at a time, and is then rammed in place in order to firm and compact the powdered material. In this way the entire refractory lining 18 is built up. At this time the crucible-like form 17 is usually removed although in certain cases it may be left in place if desired, in which case it melts into the first charge melted in the furnace.

After the above operations, it will be clear that the induction coil unit is a complete, independent unit including the inner lining and is now ready for a melting operation. I

In the completed furnace the induction coil unit just described is surrounded and protected by a strong boxlike housing reinforced with a heavy metal framework. The construction of this outside housing and framework will now be described.

The bottom refractory block 19 is preferably formed from some suitable refractory material in onepiece.

This block 19 is rectangular on the outside and isfori'ned on the top with a circular depression 20 which receives the refractory lining 18.

The bottom refractory block 19 rests on a piece of mill board 21 carried on support beams 22 preferably formed of aluminum. (Fig. 5) A wooden sill- 23 protects the lower edge of the housing along the edge on which the furnace is tilted.

The side walls of the housing are formed of pieces of mill board as follows: front wall 24, sidewallsv 25 and rear walls 26. The side walls extend past rear wall 26 to meet an extension wall 27. A space is formed between walls 26 and 27 which is used for suitable connections to the induction coil. The rear wall '26 is formed with a slot 28 through which the connections pass.

To provide attachment means for the legs 1-2, a support rnember 29 is mounted within the housing adjacent to each of the legs. The support members are also formed of mill board and have slotted openings 30 (Fig. 7) which receive bolts 31 which pass through the support member 29 and the legs 12. This slotted connection. permits adjustment and centering of the coil 10.

The bottom refractory block 19 is held in place within the housing by brackets 32 which are secured to the walls of the housing.

The furnace assembly includes a top refractory block 33 which fits within the walls of the housing and is like wise held in place by brackets 34 which engage in re-.

cesses in the top refractory block 33. The top refractory block 33 is formed with a circular opening 35 which registers with the opening in the heating. coilunit, A pouring spout 36 is fitted in the top refractory block andregisters with the opening 35.

The housing is reinforced on the outsidebyqmetal;

corner plates 37, each of which extends along two sides of the housing and is provided with extensions 38 suitably secured to the mill board as by the rivets 39.

At the front and rear of the housing, brackets 40 are attached to the extensions 38 and these brackets are held together by tie rods 41.

Additional metal reinforcing plates may be placed along the upper and lower edges of the wall elements as indicated at 42 in Figs. 2 and 3.

The metal corner plates 37 and the reinforcing plates 42 are preferablyv formed of some light-weight, nonmetallic, yet strong metal, such as an alloy of aluminum. The tie rods 41 are preferably formed of some strong, non-metallic material, such as stainless steel.

The furnace is provided with suitable trunnions which permit progressive tilting of the furnace while maintaining the pouring spout in a centered position as is well understood in the art. The front end of the furnace is provided with top trunnions 43 and with lower trunnions 44. A hoisting eyelet 45 located at the backside of the furnace provides means for attaching a suitable line to tilt the furnace. A pair of hoisting lugs 46 located on each side of the furnace permit the bodily lifting of the furnace by a crane. Each side wall of the furnace near its rear end is provided with a suitable bracket 47 which is adapted to engage a floor support to hold the furnace in its normal horizontal position during charging and melting. A rear platform 4 8 is. provided for the convenience of the workmen operating the furnace.

A pair of copper plates 49 serve as bus bars for the electrical connections.

It will be clear that in the induction melting furnace described above the housing is formed of materials-that are strong, yet relatively light in weight in order to reduce the stresses that result when the furnace is tilted. At the same time thefurnace is thoroughly braced so that it will yield as little as possible to these stresses, thus reducing materially the likelihood of cracking the. furnace lining. The framework and housing are formed of materials that do not absorb moisture, and hence there is no alternate swelling and shrinking due to this cause.

In order to' repair a cracked lining it is only necessary to remove from the housing the top refractory block, and lift out the damaged induction coil unit, A

replacement coil unit, which has been standing aside as a spare, is now dropped into the housing, and the top refractory block is then replaced. In this way the damaged furnace can be put back into operation in a very short time, instead of being down for severalweeks while the furnace is being re-wooded and re-lined.

Due to the fact that the induction coil unit is a sep: arate, independent unit, it can'be pre-dried in an oven to cure the lining 18' at any desired temperature upto about 1000 F., the temperature at which the copper tubing begins to deform. Thus it is possible to form the lining 18 of wet or dry material, or of any other suitable type, without any limitations that, would be imposed if the outer housing were in place around the coil.

According to the provisions of the patent statutes, 1- have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specificially illustrated and described.

I claimi V a 1. An electric induction furnace comprising: a boxlike. housing formed of non-combustible board, ametal spacing the individual turns of the heating coil from each. other, and means positively holding the individual turns.

of the heating coil together to permit removal of the heating coil and refractory lining as a unit from the housing.

2. A device as specified in claim 1 in which the positive spacing means includes a plurality of upright legs formed with notches, and means clamping turns of the heating coil in the notches.

3. A device as specified in claim 1 in which reinforcing members formed of non-magnetic metal extend along the vertical corners of the housing.

4. An electric induction furnace comprising: a boxlike housing formed of non-combustible board, a plurality of vertical legs removably secured to the inner walls of the housing, each of the legs being formed with a series of notches, a metal induction coil within the housing, means clamping the turns of the coil in the notches of the vertical legs to hold the coil together as a unit, whereby upon release of the legs from the housing the induction coil may be removed as a unit from the housing.

5. An electric induction furnace comprising: a boxlike housing formed of non-combustible board, the housing having a reinforced bottom, a refractory bottom block supported by the reinforced bottom, a metal induction heating coil mounted within the housing for ready removability, an inner lining of refractory material formed within the induction coil, the induction heating coil having a plurality of turns, means positively spacing the turns of the heating coil from each other and positively holding the turns of the heating coil together to permit removal of the heating coil and refractory lining as a unit from the housing, and a refractory top block removably mounted above the heating coil, the top block being formed with an opening registering with the opening of the heating coil.

6. A device as specified in claim 6 in which the positive spacing means includes a plurality of upright legs formed with notches, and means clamping turns of the heating coil in the notches.

7. A device as specified in claim 6 in which reinforcing members formed of non-magnetic metal extend along the edges of the walls of the housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,286,395 Northrup Dec. 3, 1918 1,683,986 Northrup Sept. 11, 1928 1,810,820 Davis et al. June 16, 1931 1,830,481 Northrup Nov. 3, 1931 1,842,272 Knerr Jan. 19, 1932 1,879,360 Linnhoff Sept. 27, 1932 1,895,421 Northrup Jan. 24, 1933 2,073,597 Northrup Mar. 9, 1937 2,286,481 Fisher June 16, 1942 FOREIGN PATENTS 53,500 Norway Ian. 29, 1934 

